In vitro fertilization, a medical technology by which oocyte cells are fertilized by sperms in vitro, is currently a major treatment for infertility in clinics. The standard protocols for clinical IVF practice include gametes collection, fertilization, liquid manipulation and embryo culture, with culture medium held in oil-covered drops in Petri dishes, and manipulation performed manually by pipetting. For these protocols, frequent pipetting of gametes is required, which is labor-intensive and time-consuming. Furthermore, fertilization and embryo culture require different media, therefore the zygotes have to be washed several times and transported to different drops for further development. Although some culture media have been developed to support both fertilization and embryo development (Complete HTF Medium with SSSTM, Irvine Scientific, Santa Ana, Calif.), the oocyte-washing step to remove sperm debris is still mandatory. Another issue involves the ability to track the fertilization and development of an individual oocyte, since oocytes are typically fertilized, washed, transferred and cultured in groups under the standard protocols.
Microfluidic chip has great potential for IVF. Compared with conventional IVF technology, micro-channels and micro-structures can be flexibly designed for oocytes manipulation and positioning, providing the fertilization process better controllability. Because of the advantage of integration, microfluidic chip may also integrate the process of fertilization and embryo culture on a single chip. U.S. Pat. No. 6,193,647 B1 describing oocyte trapping and IVF with such a microfluidic chip includes a constricted channel to position the oocyte, which may not only harm the oocyte by large fluid shear stress, but also is not suitable for the simultaneous positioning of multiple oocytes. PCT Publication No. WO 2005/023124 A2 describes a series of micro-wells under a narrow micro-channel, so that the oocytes could be transferred in the channel and trapped in the micro-wells. However, the device described in WO 2005/023124 A2 has several disadvantages: 1) the micro-channel in the device is too narrow, so that fast sperm sample loading or liquid manipulation processes are not available; 2) the depth of wells in the device is not optimized, considering its influence on the positioning of oocytes; 3) the device didn't overcome the problem of dead sperm and cell debris removal; and 4) the process of oocyte or embryo retrieval is based on fluid flushing or turning the device upside down, which adds complexity to the operation. In conclusion, there exists a need for a microfluidic device that integrates high-throughput single oocyte trapping, fertilization, fast liquid manipulation, embryo culture and convenient embryo retrieval.